Replying to Pickpockets!

Im traveling to France and then to london tomorrow over a span of 10 days for spring break. Now ive heard that the pickpockets are pretty bad around the popular tourist spots in france, and i assume the same for london. My question is if i catch a pickpocket in the act of tacking my wallet or his/her hand in my pocket trying to rob me, what would be the appropriate reaction to this? should i punch them in the face? or just get my wallet back if they have it and then go on with my business? so NS what do u think is the best route for such a situation?